[PATCH] Eliminate grub_CHECK_START_SYMBOL

[Pavel Roskin]

Hello!

It should be possible to compile grub for i386-pc on a pure x64_64
system with i386 support in the compiler and binutils, but without
32-bit libc or its headers.

It requires several unrelated changes.  This is the first step.  It's a
pure simplification.

The grub_CHECK_START_SYMBOL defines START_SYMBOL either as "start" or as
"_start".  But it really doesn't matter.  START_SYMBOL is only used in
kern/i386/pc/startup.S, where both "start" and "_start" are explicitly
defined labels pointing to the same code.  EXT_C(start) also expands to
"start" or "_start", so it can be replaced with "_start" as well.

ChangeLog:

        * kern/i386/pc/startup.S: Replace EXT_C(start) and START_SYMBOL
        with _start, as it's always equal to start.
        * configure.ac: Don't call grub_CHECK_START_SYMBOL.  It's not
        needed, as we no longer use START_SYMBOL.
        * aclocal.m4 (grub_CHECK_START_SYMBOL): Remove.

Index: kern/i386/pc/startup.S
===================================================================
--- kern/i386/pc/startup.S      (revision 2024)
+++ kern/i386/pc/startup.S      (working copy)
@@ -53,7 +53,7 @@
 #include <multiboot.h>
 #include <multiboot2.h>
                
-#define ABS(x) ((x) - EXT_C(start) + GRUB_BOOT_MACHINE_KERNEL_ADDR + 0x200)
+#define ABS(x) ((x) - _start + GRUB_BOOT_MACHINE_KERNEL_ADDR + 0x200)
        
        .file   "startup.S"
 
@@ -77,14 +77,14 @@
         *  These MUST be at byte offset 6 and 7 of the executable
         *  DO NOT MOVE !!!
         */
-       . = EXT_C(start) + 0x6
+       . = _start + 0x6
        .byte   GRUB_BOOT_VERSION_MAJOR, GRUB_BOOT_VERSION_MINOR
 
        /*
         *  This is a special data area 8 bytes from the beginning.
         */
 
-       . = EXT_C(start) + 0x8
+       . = _start + 0x8
 
 VARIABLE(grub_total_module_size)
        .long   0
@@ -103,7 +103,7 @@
         *  Leave some breathing room for the prefix.
         */
 
-       . = EXT_C(start) + GRUB_KERNEL_MACHINE_DATA_END
+       . = _start + GRUB_KERNEL_MACHINE_DATA_END
 
 /*
  * Support for booting GRUB from a Multiboot boot loader (e.g. GRUB itself).
@@ -202,7 +202,7 @@
 #if defined(ENABLE_LZO)
        /* decompress the compressed part and put the result at 1MB */
        movl    $GRUB_MEMORY_MACHINE_DECOMPRESSION_ADDR, %esi
-       movl    $(START_SYMBOL + GRUB_KERNEL_MACHINE_RAW_SIZE), %edi
+       movl    $(_start + GRUB_KERNEL_MACHINE_RAW_SIZE), %edi
 
        pushl   %esi
        pushl   EXT_C(grub_compressed_size)
@@ -214,7 +214,7 @@
        cld
 #elif defined(ENABLE_LZMA)
        movl    $GRUB_MEMORY_MACHINE_DECOMPRESSION_ADDR, %edi
-       movl    $(START_SYMBOL + GRUB_KERNEL_MACHINE_RAW_SIZE), %esi
+       movl    $(_start + GRUB_KERNEL_MACHINE_RAW_SIZE), %esi
        pushl   %edi
        pushl   %esi
        movl    EXT_C(grub_kernel_image_size), %ecx
@@ -239,7 +239,7 @@
        movl    EXT_C(grub_total_module_size), %ecx
        movl    EXT_C(grub_kernel_image_size), %esi
        addl    %ecx, %esi
-       addl    $START_SYMBOL, %esi
+       addl    $_start, %esi
        decl    %esi
        movl    $END_SYMBOL, %edi
        addl    %ecx, %edi
@@ -282,7 +282,7 @@
        .long   0
 
 VARIABLE(grub_start_addr)
-       .long   START_SYMBOL
+       .long   _start
 
 VARIABLE(grub_end_addr)
        .long   END_SYMBOL
@@ -510,7 +510,7 @@
  * The code beyond this point is compressed.  Assert that the uncompressed
  * code fits GRUB_KERNEL_MACHINE_RAW_SIZE.
  */
-       . = EXT_C(start) + GRUB_KERNEL_MACHINE_RAW_SIZE
+       . = _start + GRUB_KERNEL_MACHINE_RAW_SIZE
 
 /*
  *  This call is special...  it never returns...  in fact it should simply
Index: configure.ac
===================================================================
--- configure.ac        (revision 2024)
+++ configure.ac        (working copy)
@@ -383,7 +383,6 @@
     CFLAGS="$TARGET_CFLAGS -nostdlib $TARGET_IMG_LDFLAGS_AC 
-Wl,-Ttext,8000,--defsym,___main=0x8100"
   fi
   if test "x$platform" = xpc; then
-    grub_CHECK_START_SYMBOL
     grub_CHECK_BSS_START_SYMBOL
     grub_CHECK_END_SYMBOL
   fi
Index: aclocal.m4
===================================================================
--- aclocal.m4  (revision 2024)
+++ aclocal.m4  (working copy)
@@ -224,39 +224,6 @@
 AC_MSG_RESULT([$grub_cv_i386_asm_absolute_without_asterisk])])
 
 
-dnl Check what symbol is defined as a start symbol.
-dnl Written by Yoshinori K. Okuji.
-AC_DEFUN(grub_CHECK_START_SYMBOL,
-[AC_REQUIRE([AC_PROG_CC])
-AC_MSG_CHECKING([if start is defined by the compiler])
-AC_CACHE_VAL(grub_cv_check_start_symbol,
-[AC_LINK_IFELSE([AC_LANG_PROGRAM([[]],
-               [[asm ("incl start")]])],
-               [grub_cv_check_start_symbol=yes],
-               [grub_cv_check_start_symbol=no])])
-
-AC_MSG_RESULT([$grub_cv_check_start_symbol])
-
-AC_MSG_CHECKING([if _start is defined by the compiler])
-AC_CACHE_VAL(grub_cv_check_uscore_start_symbol,
-[AC_LINK_IFELSE([AC_LANG_PROGRAM([[]],
-               [[asm ("incl _start")]])],
-               [grub_cv_check_uscore_start_symbol=yes],
-               [grub_cv_check_uscore_start_symbol=no])])
-
-AC_MSG_RESULT([$grub_cv_check_uscore_start_symbol])
-
-AH_TEMPLATE([START_SYMBOL], [Define it to either start or _start])
-
-if test "x$grub_cv_check_start_symbol" = xyes; then
-  AC_DEFINE([START_SYMBOL], [start])
-elif test "x$grub_cv_check_uscore_start_symbol" = xyes; then
-  AC_DEFINE([START_SYMBOL], [_start])
-else
-  AC_MSG_ERROR([neither start nor _start is defined])
-fi
-])
-
 dnl Check what symbol is defined as a bss start symbol.
 dnl Written by Michael Hohmoth and Yoshinori K. Okuji.
 AC_DEFUN(grub_CHECK_BSS_START_SYMBOL,


-- 
Regards,
Pavel Roskin